Embedding "Easter Eggs" Into training

I'm relatively new to the Articulate community.  Recently, my team started working on a series of elearnings where we plan to embed "Easter eggs" for learners to find.  The trainings may use different formats (example one training may be in Storyline, another may be in Rise, etc). 

We decided the "Easter eggs"will give one line of a poem in each elearning with some letters in red.  In the very last elearning, the learner will need to compile all the red letters they found and arrange the letters to make a sentence based on the clues they found. 

For the first elearning we used Storyline and I embedded the "Easter eggs"into a graphic we were using.  I used a glow to kind of "help" the learner find it and placed it as a layer in the learning. So if the learner clicked on the glow it would take them to the layer with a congratulations message and provide them with the clue and instructions.

Wondering if you've embedded "Easter eggs"in your learnings? What techniques did you use?  What worked best or maybe didn't work so well?